Thin film transistor and organic light-emitting display

ABSTRACT

A thin film transistor including: a substrate; an active layer formed over the substrate; a gate insulating layer formed over the active layer; a gate electrode formed over the gate insulating layer; an interlayer insulating layer formed over the gate electrode; and source and drain electrodes that contact the active layer via the interlayer insulating layer. The source and drain electrodes may have a structure including an aluminum (Al) layer, an aluminum-nickel alloy (AlNiX) layer, and an indium tin oxide (ITO) layer, which are sequentially stacked.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 13/103,938 filed May 9, 2011, now pending, and further claimsthe benefit of Korean Patent Application No. 10-2010-0095958, filed onOct. 1, 2010, in the Korean Intellectual Property Office. The disclosureof each of U.S. patent application Ser. No. 13/103,938 filed May 9, 2011and Korean Patent Application No. 10-2010-0095958 is incorporated hereinin its entirety by reference.

BACKGROUND

1. Field

The present technology relates to a thin film transistor (TFT) and anorganic light-emitting device display including the same, and moreparticularly, to a TFT including source/drain electrodes having auniform etching profile and an organic light-emitting display includingthe TFT.

2. Description of the Related Technology

Thin film transistors (TFTs) are a particular kind of field effecttransistors manufactured by forming a semiconductor thin film on aninsulating support substrate. A TFT typically includes a gate, a drain,and a source. TFTs are generally used in sensors, memory devices, andoptical devices, and are mainly used as pixel switching devices ordriving devices of flat panel displays.

Organic light-emitting displays are typically formed of materials thatemit light when a voltage is applied thereto. Organic light-emittingdisplays have certain advantages over liquid crystal device (LCD)displays, such as a high luminance, wide viewing angles, and highresponse speeds. Organic light-emitting devices typically do not requirea backlight, and thus can be made thin. An organic light-emittingdisplay typically includes an organic light-emitting diode (OLED) and aTFT switching or driving the OLED.

The source and drain electrodes of TFTs used in organic light-emittingdisplays may have a double or triple-layered metal and/or metal oxidestack structure in consideration of emission direction, resistance,contact with an active layer, and contact with an electrode of an OLED.However, it can be difficult to etch a stack structure formed ofmaterials having different etching properties to have a uniform profileusing a single etchant.

SUMMARY

The present invention provides a thin film transistor (TFT) includingsource and drain electrodes having a stack structure with a uniformetching profile and an organic light-emitting display including the TFT.

According to an aspect of the present invention, a thin film transistorincludes: a substrate; an active layer formed over the substrate; a gateinsulating layer formed over the active layer; a gate electrode formedover the gate insulating layer; an interlayer insulating layer formedover the gate electrode; and source and drain electrodes that contactthe active layer via the interlayer insulating layer.

The source and drain electrodes include an aluminum (Al) layer, analuminum-nickel alloy (AlNiX) layer, and an indium tin oxide (ITO)layer, which are sequentially stacked. The X of the AlNiX layer mayinclude lanthanum (La). The AlNiX layer may include about 95-98 at. % ofAl, about 2-5 at. % of Ni, and about 0.2-1.0 at. % of X. The thicknessof the Al layer may be in the range of 300 Å to 1000 Å, the thickness ofthe AlNiX layer may be in the range of 3000 Å to 6000 Å, and thethickness of the ITO layer may be in the range of 50 Å to 200 Å.

The active layer may be a silicon layer.

The thin film transistor may further include a storage capacitorincluding a lower capacitor electrode, a capacitor dielectric layer, anda upper capacitor electrode on the substrate. The lower capacitorelectrode may be formed on the same layer as the active layer, thecapacitor dielectric material may be formed on the same layer as thegate insulating layer, and the upper capacitor electrode may be formedon the same layer as the gate electrode.

The thin film transistor may further include a buffer layer between thesubstrate and the active layer.

According to another aspect of the present invention, a thin filmtransistor includes: a substrate; an active layer that is formed overthe substrate and is a silicon layer having a nitrated surface; a gateinsulating layer formed over the active layer; a gate electrode formedover the gate insulating layer; an interlayer insulating layer formedover the gate electrode; and source and drain electrodes. The source anddrain electrodes contact the active layer via the interlayer insulatinglayer and include an aluminum-nickel alloy (AlNiX) layer and an indiumtin oxide (ITO) layer, which are sequentially stacked.

According to another aspect of the present invention, a thin filmtransistor includes: a substrate; an active layer formed on thesubstrate; a gate insulating layer formed on the active layer; a gateelectrode formed on the gate insulating layer; an interlayer insulatinglayer formed on the gate electrode; and source and drain electrodes. Thesource and drain electrodes contact the active layer via the interlayerinsulating layer and include an aluminum-cobalt alloy (AlCoX) layer andan indium tin oxide (ITO) layer, which are sequentially stacked.

According to another aspect of the present invention, an organiclight-emitting display includes: the thin film transistor; a pixeldefining layer that is formed on the thin film transistor and exposes adrain electrode of the thin film transistor; and an organiclight-emitting diode including an emission layer formed on the drainelectrode and the pixel defining layer and a common electrode formed onthe emission layer and the pixel defining layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail certain embodimentsthereof with reference to the attached drawings in which:

FIG. 1 illustrates a stack structure of source and drain electrodes of athin film transistor (TFT) according to an embodiment of the presentinvention;

FIG. 2 is a scanning electron microscopic (SEM) image of the stackstructure of the source and drain electrodes of FIG. 1 to show anetching profile of the stack structure;

FIG. 3 illustrates a stack structure of source and drain electrodes of aTFT according to another embodiment of the present invention;

FIG. 4 is a transmission electron microscopic (TEM) image of across-section of a structure in which an AlNiLa layer is formed on asilicon layer having a nitrated surface;

FIG. 5 illustrates a stack structure of source and drain electrodes of athin film transistor (TFT) according to another embodiment of thepresent invention;

FIG. 6 is a schematic circuit diagram of a pixel of an organiclight-emitting display according to an embodiment of the presentinvention; and

FIG. 7 is a schematic cross-sectional view of the organic light-emittingdisplay of FIG. 6.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will now be describedmore fully with reference to the accompanying drawings. However,embodiments of the invention may be embodied in may different forms andshould not construed as being limited to the descriptions set forthherein. Rather, these embodiments are provided so that the presentdisclosure is through and complete, and fully conveys the concept of theinvention to those skilled in the art. In the accompanying drawings,thicknesses and sizes of layers and regions are not drawn to scale forillustration purposes. Like reference numerals in the drawings denotelike elements.

FIG. 1 illustrates a stack structure 10 of source and drain electrodesof a thin film transistor (TFT) according to an embodiment of thepresent invention.

Referring to FIG. 1, the stack structure 10 of the source and drainelectrodes may include an aluminum (Al) layer 11, an aluminum-nickelalloy (AlNiX) layer 12, and an indium tin oxide (ITO) layer 13, whichare sequentially stacked on a silicon layer 1 that is an active layer.

The ITO layer 13, which is the uppermost layer of the source and drainelectrodes and formed of a transparent conductive metal oxide, mayfunction as an anode of an organic light-emitting diode (OLED). The ITOlayer 13 may have a thickness in the range of 50 to 200 Å. Optionally,transparent conductive metal oxides, such as indium zinc oxide (IZO),tin oxide (TO) or zinc oxide (ZnO), may be used instead of the ITO.

The AlNiX is an alloy including Al, Ni, and a small amount of metal X.The metal X may be lanthanum (La). Al improves conductivity of thesource and drain electrodes. Ni may form an AlNi₃ phase byheat-treatment to decrease interface resistance between the ITO layer 13and the AlNiX layer 12, and the metal X may inhibit the formation of Alhillocks.

The AlNiX layer 12 may efficiently reduce contact resistance between theAl layer 11 and the ITO layer 13. If the ITO layer 13 directly contactsthe Al layer 11, an Al oxide layer may be formed therebetween and thecontact resistance can increase. However, if the AlNiX layer 12 isinterposed between the Al layer 11 and the ITO layer 13, the Al oxidelayer would not form, thereby reducing the contact resistance. The AlNiXlayer 12 may reduce the contact resistance and narrow the distributionof the resistance.

The AlNiX layer 12 may contain about 95-98 at. % of Al, about 2-5 at. %of Ni, and about 0.2-1.0 at. % of the metal X. If the content of Al isless than 95% at. %, conductivity may be reduced. If the content of Niis less than 2 at. %, interface resistance against the ITO may increase.If the content of the metal X is less than 0.2 at. %, Al hillocks mayform.

The AlNiX layer 12 may have a thickness in the range of 3000 to 6000 Å.In addition, an aluminum cobalt alloy (AlCoGeX) may be used instead ofthe AlNiX. The metal X may be lanthanum (La).

The Al layer 11 may be formed of pure Al. If the AlNiX layer 12 directlycontacts the silicon layer 1, as an active layer, Al may be diffusedinto silicon at the contact region by a subsequent heat-treatment at250° C. or higher to cause a junction spike. Since the active layer intowhich Al is diffused becomes a conductor, the active layer cannotfunction as a TFT. However, if pure aluminum contacts silicon, ajunction spike would not occur by the subsequent heat-treatment at 250°C. or higher. Accordingly, the Al layer 11 can inhibit the occurrence ofa junction spike in the silicon layer 1.

In addition, if titanium (Ti) is formed on the bottom surface of theAlNiX layer 12, i.e., in an active layer/Ti/AlNiX/ITO stack structure,the ITO may protrude like a tip while etching the stack structure andthe Ti can remain on the silicon layer like a tail. The ITO tip may forma high electric field around the tip and reduce the lifespan of theOLED. Alternatively, the ITO tip may be detached from the stackstructure and become particles that generate dark spots. In addition,the Ti tail may decrease a margin of critical dimension (CD) to reducesubstantial CD of an electrode, thereby increasing resistance.

However, if the Al layer 11 is formed on the bottom surface of the AlNiXlayer 12, i.e., in an active layer/Al/AlNiX/ITO stack structure, thestack structure may be etched to have a gentle slope without an ITO tipor an Al tail. In other words, the active layer/Al/AlNiX/ITO stackstructure may form source and drain electrodes having a good profileusing a single etchant. Furthermore, the stack structure of the sourceand drain electrodes according to the present embodiment may facilitatethe development of a phosphoric acid/nitric acid/acetic acid-basedetchant to improve the etching profile.

FIG. 2 is a scanning electron microscopic (SEM) image of an Al/AlNiX/ITOstack structure 10 showing an etching profile, according to anembodiment of the present invention. The Al/AlNiX/ITO stack structure 10shown in FIG. 2 was etched using phosphoric acid, nitric acid, andacetic acid-based etchants. As shown in FIG. 2, the Al/AlNiX/ITO stackstructure 10 having a gentle positive slope may be formed on the siliconlayer 1. The lower Al layer 11 may be formed on the silicon layer 1without a tail, and the upper ITO layer 13 may be formed without a tip.

FIG. 3 illustrates a stack structure 20 of source and drain electrodesof a TFT according to another embodiment of the present invention.

Referring to FIG. 3, the stack structure 20 of the source and drainelectrodes may include an aluminum-nickel alloy (AlNiX) layer 22 and anITO layer 23, which may be sequentially stacked on a silicon layer 2that is an active layer. Also, a nitrated silicon layer 2′ may be formedon the surface of the silicon layer 2 between the silicon layer 2 andthe AlNiX layer 22.

The ITO layer 23, which is the uppermost layer of the source and drainelectrodes and is formed of a transparent conductive metal oxide, mayfunction as an anode of an OLED. The ITO layer 23 may have a thicknessin the range of 50 to 200 Å. Optionally, transparent conductive metaloxides, such as IZO, TO or ZnO, may be used instead of the ITO.

The AlNiX is an alloy including Al, Ni, and a small amount of metal X.The metal X may be lanthanum (La). Al can improve the conductivity ofthe source and drain electrodes. Ni can form an AlNi₃ phase byheat-treatment to decrease the interface resistance between the ITOlayer 23 and the AlNiX layer 22, and the metal X may inhibit theformation of Al hillocks. The AlNiX layer 22 may reduce the contactresistance and narrow the distribution of resistance.

The AlNiX layer 22 may contain about 95-98 at. % of Al, about 2-5 at. %of Ni, and about 0.2-1.0 at. % of the metal X. If the content of Al isless than 95% at. %, the conductivity may decrease. If the content of Niis less than 2 at. %, the interface resistance against ITO may increase.If the content of the metal X is less than 0.2 at. %, Al hillocks mayoccur. The AlNiX layer 22 may have a thickness in the range of 3000 to6000 Å.

The silicon layer 2 may have the nitrated surface layer 2′ formedthereon. The surface of the silicon layer 2 may be nitrated by treatingthe silicon layer 2 with plasma. The nitrated surface layer 2′ of thesilicon layer 2 may inhibit the diffusion of the Al of the AlNiX layer22 into the silicon layer 2 and causing a junction spike. In thisregard, the nitrated surface layer 2′ of the silicon layer 2 may be verythin, for example, have a thickness of about 50 Å, and thus the nitratedsurface layer 2′ would not inhibit electric contact between the sourceand drain electrodes 20 and the silicon layer 2. Also, an aluminumcobalt alloy (AlCoGeX) may be used instead of the AlNiX. The metal X maybe lanthanum (La).

FIG. 4 is a transmission electron microscopic (TEM) image of across-section of a structure in which an AlNiLa layer was formed on asilicon layer having a nitrated surface. The stack structure shown inFIG. 4 was formed by annealing at 300° C. for 30 minutes. Referring tothe TEM image of FIG. 4, the junction spike was not formed in thesilicon layer 2, because the surface 2′ of the silicon layer 2 wasnitrated and prevented the Al of the AlNiLa 22 from being diffused intothe silicon layer 2.

FIG. 5 illustrates a stack structure 30 of source and drain electrodesof a TFT according to another embodiment of the present invention.Referring to FIG. 5, the stack structure 30 of the source and drainelectrodes includes an aluminum-cobalt alloy (AlCoX) layer 32 and an ITOlayer 33, which are sequentially stacked on a silicon layer 3 that is anactive layer.

The ITO layer 33, which is the uppermost layer of the source and drainelectrodes and formed of a transparent conductive metal oxide, mayfunction as an anode of an OLED. The ITO layer 33 may have a thicknessin the range of 50 to 200 Å. Optionally, transparent conductive metaloxides, such as IZO, TO or ZnO, may be used instead of the ITO.

The AlCoX may be an alloy including Al, cobalt (Co), and a metal such asgermanium (Ge) and La. For example, the AlCoX may be AlCoGeLa. Al canimprove the conductivity of the source and drain electrodes. Co maydecrease the contact resistance of the ITO layer 33, and the Ge and Lamay inhibit the formation of Al hillocks. In other words, the AlCoXlayer 32 has excellent contact characteristics with the ITO layer 33 anddoes not cause a junction spike to occur in the interface with thesilicon layer 3.

The AlCoX layer 32 may contain about 95-99 at. % of Al, about 0.1-0.5at. % of Co, and about 0.3-1.5 at. % of the metal X. If X is GeLa, thecontent of Ge may be in the range of about 0.2 to about 1.0 at. %, andthe content of the La may be in the range of about 0.1 to about 0.5 at.%. If the content of Al is less than 95% at. %, the conductivity may bereduced. If the content of Co is less than 0.1 at. %, the interfaceresistance against ITO may increase. If the content of the metal X isless than 0.3 at. %, Al hillocks may occur. The AlCoX layer 32 may havea thickness in the range of 3000 to 6000 Å.

FIG. 6 is a schematic circuit diagram of a pixel of an organiclight-emitting display according to an embodiment of the presentinvention. Referring to FIG. 6, the pixel of the organic light-emittingdisplay includes two TFTs including a switching transistor Ts and adriving transistor Td, a storage capacitor Cst and an OLED.

The switching transistor Ts may be turned on/off through a gate line bya gate signal and may transmit a data signal received through a dataline to the storage capacitor Cst and the driving transistor Td.

The storage capacitor Cst can store the data signal transmitted from theswitching transistor Ts for one frame period. The driving transistor Tdcan generate a driving current corresponding to a voltage differencebetween the data signal stored in the storage capacitor Cst and adriving voltage (Vdd) line.

The pixel of the OLED may include an anode that is connected to anoutput terminal of the driving transistor Td and a cathode to which acommon voltage is applied, and emit light having different intensitiesaccording to the driving current of the driving transistor Td to displayan image.

Also, the pixel of the organic light-emitting display may furtherinclude a signal line in addition to the gate line and the data line anddevices in addition to the switching transistor Ts and the drivingtransistor Td.

FIG. 7 is a schematic cross-sectional view of an organic light-emittingdisplay according to an embodiment of the present invention.

Referring to FIG. 7, a buffer layer 102 is formed on a substrate 101.The substrate 101 may be formed of glass, quartz, or plastic, or anyother material, such as silicon, ceramic, or metal. The buffer layer 102may inhibit impurities, such as alkali ions from the substrate 101, frompenetrating into a TFT. The buffer layer 102 may insulate an activelayer from the substrate 101 if the buffer layer 102 contains mobileions or if a conductive substrate is used. The buffer layer 102 may beformed of silicon oxide (SiOx), silicon nitride (SiNx), siliconoxynitride (SiONx), or the like.

An active layer 111 of the switching transistor Ts, an active layer 112of the driving transistor Td, and a lower capacitor electrode 113 may beformed on the buffer layer 102. The active layers 111 and 112 may beformed of polycrystalline silicon, amorphous silicon, an oxidesemiconductor, or an organic semiconductor material. The lower capacitorelectrode 113 may be formed of the same material used to form the activelayers 111 and 112.

The active layers 111 and 112 may include drain regions 111 a and 112 aand source regions 111 b and 112 b, which may be doped with a p-typesemiconductor, and channel regions 111 c and 112 c between the drainregions 111 a and 112 a and the source regions 111 b and 112 b,respectively. In this regard, the positions of the drain regions 111 aand 112 a and the source regions 111 b and 112 b may be exchanged.

An insulating layer 121 may be formed on the active layers 111 and 112and the lower capacitor electrode 113. The insulating layer 121 may be asingle layer or a plurality of layers including a silicon oxide layer ora silicon nitride layer. The insulating layer 121 may function as a gateinsulating layer on the active layers 111 and 112 and as a capacitordielectric layer on the lower capacitor electrode 113.

Gate electrodes 131 and 132 and an upper capacitor electrode 133 may beformed on the insulating layer 121. The gate electrodes 131 and 132 maybe formed of gold (Au), silver (Ag), copper (Cu), nickel (Ni), platinum(Pt), palladium (Pd), aluminum (Al), molybdenum (Mo), tungsten (W),titanium (Ti), or an alloy thereof. The upper capacitor electrode 133may be formed of the same material used to form the gate electrodes 131and 132.

An interlayer insulating layer 136 may be formed on the gate electrodes131 and 132 and the upper capacitor electrode 133. The interlayerinsulating layer 136 may be an insulating layer formed of silicon oxideor silicon nitride.

Source and drain electrodes 141 a and 141 b of the switching transistorTs may penetrate the interlayer insulating layer 136 to contact thesource and drain regions 111 a and 111 b of the active layer 111, andsource and drain electrodes 142 a and 142 b of the driving transistor Tdmay penetrate the interlayer insulating layer 136 to contact the sourceand drain regions 112 a and 112 b of the active layer 112. The sourceand drain electrodes 141 a, 141 b, 142 a, and 142 b may include a stackstructure according to embodiments of the present invention.

A pixel defining layer 146 that exposes the drain electrode 142 a of thedriving transistor Td may be formed on the source and drain electrodes141 a, 141 b, 142 a, and 142 b and the interlayer insulating layer 136.The pixel defining layer 146 may be an organic or inorganic layer.

The stack structure 151 of the OLED may be formed to contact the drainelectrode 142 a of the driving transistor Td. The drain electrode 142 aof the driving transistor Td may function as a pixel electrode. Thestack structure 151 of the OLED may include an emission layer, and mayfurther include a hole injection layer, a hole transport layer, anelectron injection layer, or an electron transport layer.

A common electrode 161 may be formed on the stack structure 151 of theOLED. In a top-emission type display device, the common electrode 161may be formed of a transparent conductive oxide, such as ITO and IZO.The common electrode 161 may also be a thin metal layer formed of Ni orchromium (Cr) or a stack structure including a transparent conductiveoxide, such as ITO and IZO, and a metal, such as Ni or Cr. The commonelectrode 161 may function as a cathode supplying electrons into thestack structure 151 of the OLED.

Source and drain electrodes having a uniform etching profile by a singleetchant may be manufactured by changing the materials of the stackstructure of the source and drain electrodes, and an etchant for thestack structure of the source and drain electrodes may be developed.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

What is claimed is:
 1. A thin film transistor comprising: a substrate;an active layer formed over the substrate and comprising a silicon layerhaving a nitrated surface; a gate insulating layer formed over theactive layer; a gate electrode formed over the gate insulating layer; aninterlayer insulating layer formed over the gate electrode; and sourceand drain electrodes that contact the active layer through openings inthe interlayer insulating layer and comprise an aluminum-nickel alloy(AlNiX) layer and an indium tin oxide (ITO) layer, which aresequentially stacked.
 2. The thin film transistor of claim 1, whereinthe X of the AlNiX layer comprises lanthanum (La).
 3. The thin filmtransistor of claim 1, wherein the Al layer has a thickness in the rangeof 300 Å to 1000 Å and the AlNiX layer has a thickness in the range of3000 Å to 6000 Å.
 4. The thin film transistor of claim 1, furthercomprising a buffer layer between the substrate and the active layer. 5.A thin film transistor comprising: a substrate; an active layer formedover the substrate; a gate insulating layer formed over the activelayer; a gate electrode formed over the gate insulating layer; aninterlayer insulating layer formed over the gate electrode; and sourceand drain electrodes that contact the active layer through openings inthe interlayer insulating layer and comprise an aluminum-cobalt alloy(AlCoX) layer and an indium tin oxide (ITO) layer, which aresequentially stacked.
 6. The thin film transistor of claim 5, whereinthe X of the AlCoX layer comprises germanium (Ge) and lanthanum (La). 7.The thin film transistor of claim 6, wherein the AlCoX layer comprisesabout 95-99 at. % of Al, about 0.1-0.5 at. % of Co, about 0.2-1.0 at. %of the Ge, and about 0.1-0.5 at. % of La.
 8. The thin film transistor ofclaim 5, wherein the AlCoX layer has a thickness in the range of 3000 Åto 6000 Å and the ITO layer has a thickness in the range of 50 Å to 200Å.
 9. The thin film transistor of claim 5, wherein the source and drainelectrodes further comprise an Al layer between the AlCoX layer and theactive layer.
 10. The thin film transistor of claim 5, wherein theactive layer is a silicon layer or a silicon layer having a nitratedsurface.